Extreme pressure lubricants containing sulfur



United States Patent Robert H. Davis, Pitman, N.J., assignor to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Mar. 23, 1965, Ser. No. 442,178 17 Claims. (Cl. 252-40.7)

This invention relates to novel lubricating compositions having excellent extreme pressure properties. More particularly, it is directed to lubricating compositions containing additives which in combination synergistically improve the extreme pressure characteristics of these compositions.

Lubricating compositions, especially those used in metal working, heavy industrial machinery and marine diesel applications, are not always adapted to withstand the high pressures encountered therein. The lubricant must be operative under high temperatures and pressures, carry away solid impurities, dissipate the heat evolved, and at the same time chemically resist the deteriorating conditions encountered in such operations. At high temperatures, moreover, mineral oils may become oxidized and form corrosive acids which can damage the metal surfaces of the metal being worked or of the machines or engines.

It has heretofore been the practice to improve the strength of lubricating compositions under extreme pressure conditions by adding a metal carboxylate, such as calcium acetate. Unfortunately, however, even the presence of these known extreme pressure agents do not always adequately improve the properties of lubricating compositions.

Accordingly, it is an object of this invention to provide improved lubricating compositions for use in extreme pressure conditions. Another object is to provide lubricating oil compositions containing combined additives for improved extreme pressure characteristics.

The aforementioned and other objects I achieve by adding to a lubricant, an alkaline earth metal salt of a C to C -alkyl carboxylic acid in the presence of a sulfur-containing material. Surprisingly, the combination of these two additives provides unexpectedly enhanced extreme pressure properties over each additive used alone. The resulting lubricating compositions of this invention display such excellent extreme pressure results, that the combination evidences synergism. The weight amounts of each additive in the lubricant may vary, however, effective amounts of metal carboxylate and sulfur compound are in the ranges of about 0.01% to 50% of the carboxylate and about 0.1% to 30% of sulfur compound; especially useful amounts are in the ranges of about 0.5% to 20% of carboxylate and about 0.5 to 15% of sulfur compound.

Preferably, the salts of carboxylic acids having from 1 to 3 carbon atoms are combined with sulfur compounds which include elemental sulfur; alkyl sulfides, disulfides and polysulfides, wherein the number of carbon atoms in each alkyl group is in the range of l to 22 and the number of sulfur atoms is in the range of 1 to aromatic sulfides and polysulfides, wherein the aromatic ring may be substituted by alkyl groups having a total of 1 to 22 alkyl carbon atoms and the number of sulfur atoms is in the range of l to 10; and sulfurized fatty carboxylates, alcohols and esters, such as sulfurized oils and fats having a sulfur content of up to about 20% An important benefit in adding metal salts to the lubricating oil is the presence of the basic metal ions which are useful in combating the effect of acids forming in the lubricating oil during operation. For this purpose, the lower carboxylic acid salts, such as the calcium, rnagnesium and barium salts of formic acid, acetic acid and 3,278,432 Patented Oct. 11, 1966.

propionic acid are preferred, and the most preferred salt is calcium acetate. The salt, moreover, may be either anhydrous or hydrated. If desired, the salt may also be formed in the lubricant in situ, even in the presence of the sulfur compound, as well as using a preformed additive. The carboxylic acid or the anhydride may be added to the lubricant followed by the oxide or hydroxide of the metal, i.e. acetic anhydride and calcium hydroxide, and the reaction mass is then heated to form the carboxylate.

The dispersion of these oil-insoluble alkaline earth metal salts in the lubricant may be obtained by use of mechanical mixing, such as homogenizers and blenders. However, it may be desirable to use a dispersion stabilizer, preferably a long-chain fatty acid, from about 4 to 24 carbon atoms, such as oleic acid, as described in US. Patent No. 3,121,689, and more preferably an N-acyl sarcosine compound, such as oleyl sarcosine, as described in US. patent application Serial No. 120,938, now US. Patent No. 3,182,020. The acyl group of the sarcosine compound in that disclosure contains from 9 to 25 carbon atoms. The presence of these stabilizers may also have a thickening effect on the lubricant. Thus, using the sarcosine compound to control the consistency of the composition, it is possible to obtain lubricating compositions ranging from fluid oils to greases. The calcium acetate dispersions in oil, using a stabilizer, are readily obtained by using known techniques.

With respect to the sulfur-containing material, or sulfur compound, which may be used in employing this invention, as indicated previously, the term includes elemental sulfur and organic sulfur compounds. Elemental sulfur includes sulfur powders having any of the allotropic forms; flowers of sulfur are preferred since the powder is very finely divided and hence more easily dispersed. According to this invention, the term alkyl sulfides includes dialkyl sulfides and disulfides, unsymmetrical alkyl sulfides, disulfides, and polysulfides in which the alkyl groups have carbon atoms ranging from 1 to 20. Aromatic sulfides include phenyl sulfides and the substitutedaryl polysulfides; the preferred of these aromatic sulfides is dibenzyl disulfide. These sulfides may contain up to about 10 atoms of sulfur per mole of sulfide.

The sulfur compounds of this invention also embrace those described in US. Patent No. 2,993,858. Suitable compounds are the corrosive, sulfur-containing organic compositions in which sulfur is loosely-bound, including sulfurized animal, marine or vegetable oils containing from about 12% to about 20% by Weight of sulfur; sulfurized mineral oils, including the naphthenic and parafiinic oils, containing up to about 5% of added sulfur; and sulfurized terpenes and mercaptans. Of particular utility are the corrosive, sulfurized lard and sperm oils containing about from 12% to 20%, and preferably about 15% by weight of sulfur.

Also included are the so-called non-corrosive sulfurized substances which are characterized as firmly bound (as opposed to the loosely-bound above). These substances include sulfurized animal, marine, and vegetable oils containing up to about 10% by weight of sulfur, such as sulfurized lard and sperm oils.

A wide variety of lubricating oils can be used as the base for the lubricants described herein, including solvent refined mineral oils. Suitably the above mentioned sulfurized mineral oils, preferably corrosive sulfurized mineral oils, may themselves be used as the base oil. In such a case, the base oil may contain from about 0.1% to about 5% by weight of loosely bound sulfur, prepared by sulfurizing a mineral oil (having a viscosity range of 40300 SUS at F.) using known techniques.

Of interest in preparing the novel additive combination of this invention is a concentrated oil preparation containing a relatively small amount of lubricating oil carrier, sufficient to maintain the salt dispersion and from 30 to 60 percent by weight of the combined salt, stabilizer, and sulfur compound. This concentrate may be easily added to any desired lubricant prior to use.

EVALUATION OF ADDITIVES The standard tests for illustrating extreme pressure effects on lubricant oil compositions are the four-ball and the tapping tests.

A. The four-ball test is conducted as follows: three one-half inch 52-100 tool-steel balls are clamped in a stationary ball cup. A fourth ball is held in a rotatable chuck at the vertical end of a spindle and is rotated against the three stationary balls using the test compositions as the lubricant. A series of runs are made with increasing loads (using increments of 10 kg.) until the balls become welded. The higher the load at which the weld occurs, the more efficient is the lubricant tested.

Examples 1 to 3 TABLE I Sulfur Calcium Oil, Percent Four-Ball Example Powder, Acetate, Wt. Weld Load,

Percent Wt. Percent Wt. kg.

90 390 10 90 210 5 90 over 620 Examples 4 to 6 It has been observed that calcium acetate tends to separate out of the dispersions of Example 1 after a period of storage time. In this example, a dispersion stabilizer was added to the lubricating oil to maintain the salt in the dispersed state. In this second series of dispersions, a premixed dispersion containing 40% by weight of calcium acetate, 3% by weight of n-oleoyl sarcosine and 57% by weight of the above oil was prepared. This material is referred to as (4) Dispersion A. Dispersion A was combined in lubricating compositions with (6) an alkylpolysulfide, i.e. ditertiarynonyl polysulfide (DTNPS) containing approximately 40% sulfur. The polysulfide was also tested alone (5). The following tabulated results were obtained from the four-ball test machine:

Examples 7 to Representative of aromatic sulfides, (7) di'benzyl disulfide was tested on the four-ball test machine wit-h (8) calcium acetate and (9) the pre-stabilized Dispersion A described above. The results are tabulated in Table III.

- B. The ability of a cutting oil to operate efliciently is measured in the tapping test. In the tapping test, a series of holes is drilled in a test metal such as SAE 1020 hotrolled steel. The holes are tapped in a drill press equipped with a table which is free to rotate about the center on ballbearings. A torque arm is attached to this floating table and the arm in turn activates a spring scale, so that the actual torque during the tapping, with the oil being evaluated, is measured directly. The same conditions used in evaluating the test oil are employed in tapping with a strong oil which has arbitrarily been assigned an etficiency of The average torque in the test oil is compared to that of the standard and a relative efficiency is calculated on a percentage basis. For example,

Torque with standard reference oil 19.3 Torque with test oil 19.8 Relative efficiency of test oil 19.3/19.8 100=97.4

This test is described by C. D. Flemming and L. H, Sudholz in Lubrication Engineering, volume 12, No. 3, May- Juue 1956, pages 199 to 203.

Examples 10 to 14 The tapping test efiiciency of a series of lubricating compositions was obtained using the above-described test. To the lubricant was added an additive concentrate (Concentrate A) containing 20% calcium acetate, 0.2% water, 5% oleic acid and 74.8% of a sulfurized lard oil containing 15% by weight of sulfur. This sulfurized lard oil is disclosed as an extreme pressure agent for lubricating oils.

This concentrate was obtained by adding all of the above ingredients together in a drill-press kettle and heating the contents to 280 F. The contents are then allowed to cool to room temperature under agitation.

The above-defined Concentrate A was added to a sulfurized, naphthenic mineral oil having an SUS viscosity of seconds at 100 F. and containing about 1% by weight of added sulfur. Various combinations of the concentrate, the sulfurized lard oil and the sulfurized naphthenic oil were tested by the tapping test. The results are tabulated below.

TABLE IV Concentrate sulfurized sulfurized Tapping Test Example A, Percent Lard Oil, Oil, Percent Efficiency,

Wt. Percent Wt. Wt. Percent The sulfurized lard oil described above was tested alone (13) in the mineral oil of the earlier examples in the four-ball test machine and in the presence of Dispersion smaasa The data in the five tables indicate that the combined presence of alkaline earth metal carboxylates and sulfur, regardless of whether the sulfur is present as an element or in a compound, provides lubricating oils with unexpectedly higher extreme pressure properties than either of the two ingredients alone. The test results of the preferred calcium acetate-sulfur compositions strongly indicate the presence of a synergistic cooperation.

The amount of alkaline earth metal carboxylate salts which may be used in my novel lubricating composition ranges from about 0.01% to about 50% by weight and preferably 0.5 to 20% of total composition. The sulfur content may range from about 0.1% to about 30% by weight and preferably 0.5% to 15% of total composition.

Also added to the lubricating oil composition may be other types of additives which provide further desirable properties to the composition. These include viscosity index improvers, pour point controlling agents, detergents, antioxidants and the like.

The hereinabove description is intended to illustrate my invention and not to limit any aspect thereof except as indicated in the appended claims.

I claim:

1. A lubricating composition consisting essentially of a major amount of a lubricating oil and a minor amount sufficient to provide improved extreme pressure properties thereto of an alkaline earth metal salt of a C to C carboxylic acid and a sulfur-containing material selected from the group consisting of sulfur, alkyl sulfides, alkyl polysulfides, aromatic sulfides and aromatic polysulfides and sulfurized oils and fats.

2. The lubricating composition of claim 1, wherein the said carboxylic acid contains from 1 to 3 carbon atoms.

3. A lubricating composition consisting essentially of a lubricating oil and of from about 0.01% to about 50% by weight of an alkaline earth metal salt of a carboxylic acid having from 1 to 3 carbon atoms, and from about 0.1% to about 30% by weight of a sulfur-containing material selected from the group consisting of sulfur, alkyl sulfides and alkyl polysulfides, aromatic sulfides, aromatic polysulfides, and alkyl-substituted derivatives thereof, wherein the alkyl groups :in each instance contain from 1 to 22 carbon atoms, said sulfides having from 1 to sulfur atoms per mole, sulfurized oils and sulfurized fats, wherein the sulfur content is up to about 20%.

4. A lubricating oil composition consisting essentially of a mineral oil and from about 0.5 to about 20% by weight of alkaline earth salt of a carboxylic acid containing 1 to 3 carbon atoms and from 0.5% to about by weight of a sulfur-containing material selected from the group consisting of sulfur, alkyl sulfides and alkyl polysulfides, aromatic sulfides, aromatic polysulfides, and alkyl-substituted derivatives thereof, wherein the alkyl groups in each instance contain from 1 to 22 carbon atoms said sulfides having from 1 to 10 sulfur atoms per mole, sulfurized oils and sulfurized fats.

5. The composition of claim 4 wherein the sulfurized oils are sulfurized mineral oils containing up -to 5% sulfur.

6. The composition of claim 4 wherein the sulfurized fats are selected from the group consisting of sulfurized lard oils and sulfurized sperm oils containing from 12% to sulfur.

7. A lubricating oil composition consisting essentially of a lubricating oil, from about 0.5% to about 20% by weight of calcium acetate and from about 0.5 to about 15 by weight of a sulfur-containing material selected from the group consisting of sulfur, ditertiary-nonylpolysulfide, dibenzyl disulfide, sulfurized lard oil containing from about 12% to about 20% by weight of sulfur, and sulfurized mineral oil containing from about 0.1% to about 5% by weight of sulfur.

8. A lubricating oil composition consisting essentially of a major amount of a mineral oil and a minor amount sufiicient to provide improved extreme pressure properties thereto of a mixture of calcium acetate and sulfur.

9. A lubricating composition consisting essentially of a major amount of a lubricating oil and a minor amount suflicient to provide improved extreme pressure properties thereto of a mixture of an alkaline earth carboxylate salt containing 1 to 3 carbon atoms and a dispersion stabilizer and a sulfur-containing material selected from the group consisting of sulfur, alkyl sulfides and alkyl polysulfides, aromatic sulfides, aromatic polysulfides, and alkyl-substituted derivatives thereof, wherein the alkyl groups in each instance contain from 1 to 22 carbon atoms, and sulfurized oils and fats containing up to 20% sulfur.

10. The composition of claim 9, wherein the dispersion stabilizer is selected from the group consisting of a longchain fatty acid containing from about 4 to 24 carbon atoms and an N-acyl sarcosine compound wherein the acyl group'contains from about 9 to 25 carbon atoms.

11. The composition of claim 10, wherein the dispersion stabilizer is oleic acid.

12. The composition of claim 10, wherein the dispersion stabilizer is N-oleyl sarcosine.

13. A lubricating composition consisting essentially of a mineral oil and a mixture of an alkaline earth carboxylate having from 1 to 3 carbon atoms, a dispersion stabilizer, and a sulfur-containing material selected from the group consisting of sulfur, alkyl sulfides, alkyl polysulfides, aromatic sulfides, aromatic polysulfides, sulfurized oils, and sulfurized fats, said composition containing about 0.01% to 50% by weight of carboxylate and about 0.1% to 30% by weight of sulfur-containing compound.

14. A lubricating composition consisting essentially of a major amount of a mineral oil and a minor amount sufficient to provide improved extreme pressure properties thereto of a mixture of calcium acetate, N-oleoyl sarcosine, and ditertiarynonylpolysulfide.

15. A lubricating composition consisting essentially of a major amount of a lubricating oil and a minor amount sufficient to provide improved extreme pressure properties thereto of a mixture containing calcium acetate, oleic acid and a sulfurized lard oil containing about 15 by weight of sulfur.

16. A lubricating composition consisting essentially of a major amount of a sulfurized mineral oil containing about 1% by weight of sulfur, and a minor amount sufiicient to provide improved extreme pressure properties thereto of a mixture of calcium acetate, oleic acid, and a sulfurized lard oil containing about 15% by weight of sulfur.

17. A lubricating composition consisting essentially of a major amount of a mineral oil and a minor amount sufficient to provide improved extreme pressure properties thereto of a mixture containing calcium acetate and dibenzyl disulfide.

References Cited by the Examiner UNITED STATES PATENTS 2,160,577 5/1939 Maag 252-31 X 2,929,778 3/1960 Manteuifel et a1. 25224 2,941,945 6/ 1960 Fainman et a1 25231 X 2,993,858 7/1961 Sudholz 25232.7 3,007,870 11/1961 OI-Ialloran 25240.7 3,121,689 2/1964 Davis 25240.5

3,182,020 5/ 1965 Davis 25240.7

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Examiner. 

1. A LUBRICATING COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF A LUBRICATING OIL AND A MINOR AMOUNT SUFFICIENT TO PROVIDE IMPROVED EXTREME PRESSURE PROPERTIES THERETO OF AN ALKALINE EARTH METAL SALT OF A C1- TO C4CARBOXYLIC ACID AND A SULFUR-CONTAINING MATERIAL SELECTED FROM THE GROUP CONSISTING OF SULFUR, ALKYL SULFIDES, ALKYL POLYSULFIDES, AROMATIC SULFIDES AND AROMATIC POLYSULFIDES AND SULFURIZED OILS AND FATS. 